The use of cellular text messaging services (CTMS), such as the Short Message Service (SMS) available for GSM, for various purposes is known. Typically, one of two scenarios is employed. In a first scenario, a message is defined by the sender and communicated to the recipient, as the entire communication. In a second scenario, the sender sends a code to the recipient, which then responds with corresponding information to the sender. Thus, a typical CTMS communication involves only two parties, though multiple recipients of a message or broadcast were contemplated.
SMS was originally designed as part of GSM, but is now available on a wide range of networks, including 3G networks. However, not all text messaging systems use SMS, and some notable alternate implementations of the concept include J-Phone's SkyMail and NTT Docomo's Short Mail, both in Japan. E-mail messaging from phones, as popularized by NTT Docomo's i-mode and the RIM BlackBerry, also typically use standard mail protocols such as SMTP over TCP/IP.
Transmission of the short messages between SMSC and phone can be done through different protocols such as SS7 within the standard GSM MAP framework or TCP/IP within the same standard. Messages are sent with the additional MAP operation forward_short_message, whose payload length is limited by the constraints of the signaling protocol to a maximum of 140 bytes (140 bytes=140*8 bits=1120 bits). In practice, this translates to either 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters. Routing data and other metadata is additional to the payload size.
A Short Message Service Center (SMSC) is a network element in the mobile telephone network which delivers SMS messages. When a user sends a text message (SMS message) to another user, the phone actually sends the message to the SMSC. The SMSC stores the message and then delivers it to the destination user when they are available. This is a store and forward operation. The SMSC usually has a configurable time limit for how long it will store the message, and users can usually specify a shorter time limit if they want. For bulk transmission and reception of SMS messages, SMSCs have conventional, fixed, network interfaces as well as mobile network interfaces. A number of protocols have been defined to support this sort of wire-line access:
SMPP (Short message peer-to-peer) The most common protocol and the only non-proprietary one in wide use.
EMI/UCP (External Machine Interface/Universal Computer Protocol). A proprietary protocol by market leader LogicaCMG.
CIMD (Computer Interface to Message Distribution). A proprietary protocol developed by Nokia for its Artuse SMSC.
OIS (Open Interface Specification). Despite the name, a proprietary protocol developed by Sema Group (now Airwide Solutions).
Larger content (known as long SMS or concatenated SMS) can be sent segmented over multiple messages, in which case each message will start with a user data header (UDH) containing segmentation information. Since UDH is inside the payload, the number of characters per segment is lower: 153 for 7-bit encoding, 134 for 8-bit encoding and 67 for 16-bit encoding. The receiving phone is then responsible for reassembling the message and presenting it to the user as one long message. While the standard theoretically permits up to 255 segments, 6 to 8 segment messages are the practical maximum, and long messages are billed as equivalent to multiple SMS messages.
Short messages can also be used to send binary content such as ringtones or logos, as well as OTA programming or configuration data. Such uses are a vendor-specific extension of the GSM specification and there are multiple competing standards, although Nokia's Smart Messaging is by far the most common.
SMS is also used for machine to machine communication. For instance, there is an LED display machine controlled by SMS, and some vehicle tracking companies like ESITrack use SMS for their data transport or telemetry needs.
SMS is widely used for delivering premium content such as news alerts, financial information, logos and ring tones. Such messages are also known as premium-rated short messages (PSMS). The subscribers are charged extra for receiving this premium content, and the amount is typically divided between the mobile network operator and the content provider (VASP) either through revenue share or a fixed transport fee.
Premium short messages are also increasingly being used for “real-world” services. For example, some vending machines now allow payment by sending a premium-rated short message, so that the cost of the item bought is added to the user's phone bill or subtracted from the user's prepaid credits.
A new type of “free premium” or “hybrid premium” content has emerged with the launch of text-service websites. These sites allow registered users to receive free text messages when items they are interested go on sale, or when new items are introduced.